Overbased magnesium sulphonate composition

Abstract

Overbased magnesium sulphonates having increased resistance to interactions are prepared from sulphonic acids prepared from alkylates with long and medium chain alkyl groups. Compositions comprising such overbased magnesium sulphonate are particularly suitable for use in combination with high molecular weight dispersants and/or friction modifiers. Stable sediment-free lubricating oil compositions (including lubricants and concentrates therefor) can be prepared which can meet SG quality and the Tier II fuel economy requirements.

We claim: 
     
       1. A lubricating oil meeting the SG quality level in the American Petroleum Institute Engine Service Categories for service station oils and/or providing American Petroleum Institute Tier II fuel economy performance, which lubricating oil comprises an overbased magnesium sulphonate composition comprising: (A) At least one magnesium alkyl aryl sulphonate containing 1 to 3 alkyl groups, one of which alkyl groups contains an average number of carbon atoms of at least 40 therefor while any remaining alkyl groups contain less than 10 carbon atoms, and   (B) at least one magnesium alkyl aryl sulphonate containing 1 to 3 alkyl groups, one of which alkyl groups contains an average number of carbon atoms of 10 to 33 while any remaining alkyl groups contain less than 10 carbon atoms.   
     
     
       2. The lubricating oil according to claim 1, in which the aromatic group in the alkyl aryl sulphonates is a benzene, toluene or naphthalene group. 
     
     
       3. The lubricating oil according to claim 1, in which component (A) makes up 10 to 40 wt % of the overbased magnesium sulphonate composition, the balance being (B). 
     
     
       4. The lubricating oil according to claim 1, in which one of the alkyl groups in component (A) is a branched alkyl group which contains an average number of carbon atoms of at least 50. 
     
     
       5. The lubricating oil according to claim 1 in which the component (B) is selected from the group consisting of (B1) sulphonates containing a C 15  to C 40  branched chain alkyl group, having an average number of carbon atoms of 15 to 33, (B2) sulphonates containing a C 10  to C 30  straight chain alkyl group, and mixtures thereof. 
     
     
       6. The lubricating oil according to claim 5, in which (B2) contains C 15  to C 15  straight chain alkyl groups. 
     
     
       7. The lubricating composition according to claim 5, comprising 10 to 40 wt % of component (A), 10 to 60 wt % of component (B1), and 10 to 40 wt % of component (B2). 
     
     
       8. The lubricating oil according to claim 1, in which the overbased magnesium sulphonate is post-treated with a carboxylic acid and/or a glycol to improve the water tolerance and/or stability and/or foaming performance and/or seal compatibility thereof. 
     
     
       9. The lubricating oil according to claim 1, in which the overbased magnesium sulphonate composition has a total base number as measured by ASTM D2896 of at least 300. 
     
     
       10. The lubricating oil according to claim 1 which further comprises at least one additive selected from the group consisting of an ashless dispersant, a friction modifier, a copper compound as antioxidant, a zinc dihydrocarbyl dithiophosphate, other conventional additives. 
     
     
       11. The lubricating oil according to claim 1, which contains from 0.01 to 5 wt % of overbased magnesium sulphonate. 
     
     
       12. A concentrate for use in formulating a lubricating oil which comprises up to 50 wt % of an overbased magnesium sulphonate composition comprising: (A) at least one magnesium alkyl aryl sulphonate containing 1 to 3 alkyl groups, one of which alkyl groups contains an average number of carbon atoms of at least 40 while any remaining alkyl groups contain less than 10 carbon atoms, and   (B) at least one magnesium alkyl aryl sulphonate containing 1 to 3 alkyl groups, one of which alkyl groups contains an average number of carbon atoms of 10 to 33 while any remaining alkyl groups contain less than 10 carbon atoms.